Signs of a Hidden Water Leak, and the Two-Minute Test That Confirms One

Which signs of a hidden water leak show up first?

The bill usually talks before the house does. Water escaping under a slab or inside a wall has somewhere to go, so the first clue is often a usage number on the LADWP statement that climbed for a second month while nothing changed.

The house catches up in its own order. A faint hiss with every tap closed, a warm floor tile, a swollen baseboard, bubbling paint, or a musty smell in a closet each point at water moving where it should not. Low pressure at every fixture at once means the loss sits upstream, on the service line or at the regulator.

What each symptom usually points to

No single row settles anything on its own. The value is in the pairing: a high bill plus a moving meter, or a warm floor plus a heater that never rests. The meter test below turns suspicion into evidence.

How does the meter test work, step by step?

You can confirm a leak before calling anyone, and the result shapes the whole visit. The test needs the house quiet, so pick a moment when nobody will flush, shower, or run the dishwasher for half an hour.

1. Turn off every fixture and appliance that uses water. That means faucets, the ice maker, the washing machine, the irrigation controller, and the pool autofill if you have one.

2. Find the meter box at the curb or sidewalk, lift the lid, and wipe the face of the meter so you can read it.

3. Watch the small triangle or star on the dial for two full minutes. Some newer digital meters show a dripping-faucet icon instead when flow never stops.

4. Write down the full reading, wait 30 minutes with no water used, and read it again. Any difference is water you paid for and never used.

5. Close the main shutoff where the line enters the house and watch the dial again. Still moving means the leak sits in the yard or the irrigation. Stopped means it sits inside or under the house.

Tell us what you saw, including how fast the dial moved. We then start the visit knowing which half of the property to test first. That head start is the difference between a quick pressure check and an afternoon of hunting.

Why is the bill up when nothing changed?

Rule out the honest causes first. A new sprinkler schedule, a filled pool, house guests, and a rate change all move the bill without a leak. Compare the usage figures on the statement, not the dollar totals, since usage is the number a leak changes.

If usage climbed and habits did not, look at the toilets before anything else. A flapper that no longer seals lets water trickle from the tank to the bowl around the clock, and the meter counts every drop. Put a few drops of food coloring in the tank and wait fifteen minutes without flushing. Color in the bowl means the flapper is leaking.

The EPA puts household leaks at nearly 10,000 gallons a year for the average family. It also says one home in ten has leaks wasting 90 gallons or more a day. Most of that is toilets and dripping fixtures, which is good news, since those are quick to fix compared with anything under a slab.

What does a warm floor spot mean?

A warm patch on the floor, with no heater vent or window to explain it, is the classic sign of a hot-side slab leak. Thousands of San Fernando Valley homes from the 1950s through the 1970s have copper supply lines cast into the slab. Hot water corrodes copper faster than cold. When a hot line pinholes, the escaping water warms the concrete above it.

Two companions confirm it. The water heater runs more than it used to, since it heats water that never reaches a tap. Hot water also takes longer to arrive at the shower. A quick test: close the cold-water valve on top of the water heater and check the meter. If the dial stops, the leak is on the hot side.

Slab leaks head down, not into the room, so bills climb long before a floor shows anything. The fix is a slab leak repair, either a spot repair through one small opening or a reroute overhead that abandons the failed line. Cracks in tile, a lifting floor, or a doorway that sticks mean the leak has run a long time.

Musty smell, low pressure, and the sound of running water

A musty smell in one room, one closet, or the cabinet under a sink means damp material behind a surface. Mold needs only about two days of moisture to get started. Treat the smell as a reason to look now. Pull the cabinet contents, check the supply lines and the drain trap, and press the drywall around the baseboard for softness.

Low pressure tells you where to look by how widespread it is. One weak faucet is almost always a clogged aerator. Weak pressure at every fixture points upstream, to a failing pressure regulator or to the buried water line from the meter. The regulator is the simpler part to test first.

Hissing or the sound of water moving with every fixture closed is worth chasing at night, when the house is quiet. Put an ear to the wall near the water heater, the kitchen, and each bathroom. Pressurized water escaping through a pinhole makes a steady hiss, and the loudest spot is usually within a few feet of the leak.

Slab, wall, or yard: where is the leak?

The meter test with the house valve closed makes the first cut. A dial that keeps moving puts the loss outside: the service line from the meter, the irrigation system, or a pool fill line. A dial that stops puts it inside the building, in a wall, under a floor, or beneath the slab.

Yard leaks leave their own tracks. A green stripe of lawn in a dry August, a soft patch of ground, or a dip in the driveway trace the service line. Wall leaks show as stains, bubbling paint, swollen baseboards, and that musty smell. Slab leaks give the warm floor, the hissing, and the water heater that never rests.

Ownership matters for the outdoor case. LADWP owns the pipe from the street main to the meter, and you own everything from the meter to the house. A leak on the house side of the meter is your repair. Inside a wall, water often shares the cavity with wiring. Wet drywall around an outlet is an electrical problem as well as a plumbing one.

What do acoustic and thermal detection actually do?

Once the meter test says inside, the job is to find one pinhole in a pipe you cannot see without turning the house into Swiss cheese. Four tools do that from the surface.

• Acoustic listening: a ground microphone picks up the hiss of pressurized water leaving the pipe. The loudest point along the line marks the leak, often within a foot.
• Thermal imaging: an infrared camera shows the warm trail a hot-water leak leaves across a slab or up a wall. That narrows the search before anyone listens.
• Pressure isolation: closing valves one section at a time and watching a gauge names the guilty branch, house, irrigation, or pool, without opening anything.
• Dye testing: harmless dye traces leaks in toilets, shower pans, and pool fittings that pressure tools cannot tell apart.

No single tool wins every job. A cold-side slab leak leaves no heat trail, a deep yard line can be silent at the surface, and plastic pipe carries sound poorly. A good crew cross-checks with a second method before marking the floor. Current ranges for a detection visit are on our leak detection page, and the search itself opens nothing.

When should you stop watching and call?

Call as soon as the meter moves with everything off, since the signs of a hidden water leak never improve on their own. Water under a slab or inside a wall does not fix itself. A slow leak that runs for months does more damage in flooring, drywall, and mold than the repair ever would. If water is actively pooling, close the main house valve first, then pick up the phone. A live person answers (818) 421-5290 around the clock.

Original copper from the 1950s and 1960s seldom stops at one pinhole. Mineral-heavy water and stray electrical current eat copper from the inside, and once the first pinhole opens, more usually follow. One leak in otherwise solid pipe earns a spot repair. A second or third within a year is the house asking for whole-house repiping. The pipe wall we see at the repair opening tells us which case you have.

Our Los Angeles plumber team locates the leak, marks it, and puts the repair in writing before anything gets cut. The crew that finds it can fix it with your approval. If you would rather have a licensed electrician and plumber in Los Angeles read the meter with you, that is a fair start too.

Frequently asked questions